It has been known for a long time to make use of devices for blowing gas onto one or both faces of a traveling metal strip, in particular in order to cool it.
Reference may thus be made to documents U.S. Pat. No. 3,116,788 and U.S. Pat. No. 3,262,688 which describe different systems for blowing gas from hollow boxes or tubular hollow elements disposed in the longitudinal direction of the strip or in a direction extending transversely to the strip travel direction. Those documents teach using jets of gas that are inclined relative to the normal to the plane of the traveling strip in order to improve the stability of the strip as it travels.
More recently, as described in document WO-A-01/09397, proposals have been made to channel the stream of blown gas by providing boxes fitted with blow tubes, with the blow tubes inclined towards the edges of the strip, mainly for the purpose of avoiding vibration in the traveling strip while it is being cooled by blowing jets of gas.
Document U.S. Pat. No. 6,054,095 also teaches inclining blow tubes fitted to the boxes towards the edges of the strip, the arrangement of the blow tubes being selected to obtain better temperature uniformity of the strip.
The various documents mentioned above seeking to improve temperature uniformity of the strip in a transverse direction are of interest, but without in any way solving the problems that arise in the zone of the free margins of the traveling strip.
These problems are both thermal, insofar as edge effects make it difficult to obtain uniform temperature, and also aerodynamic, insofar as the jets of gas blown from the two boxes disposed on either side of the traveling strip create turbulence that disturbs both the stability of the strip and the uniformity of the atmosphere in the vicinity of the free margins of said traveling strip.
The above-mentioned problems become more complicated when there are changes in strip format, in particular in strip width.
When changing from a wide strip to a narrower strip, it is naturally advantageous to be in a position, supposing this is possible, to limit the blowing of gas in the marginal zones between which traveling strip no longer passes.
In an attempt to solve that problem, proposals have already been made to subdivide the inside of the box and its feed pipe, by arranging stationary partitions to define inside spaces having downstream ends located at the inlets of the tubular nozzles for injecting gas. The upstream end of each of said inside spaces receives a flow rate regulator member, e.g. of the rotary valve type. Under such circumstances, if the two valves associated with the spaces that open out in the margins are closed and if the other valves are opened, then blowing occurs only in the central outlet zone from the hollow box. Nevertheless, in practice such a system is found to be very constraining because it is very frequent that a strip lies astride two adjacent spaces, such that it is always necessary to open the extreme valve, while it is traveling, since the strip may move as much as 100 millimeters (mm) on either side of its central position, in a transverse direction. Thus, if it is desired to preserve good uniformity of cooling, it is necessary to ensure that the blow width is always excessive, and consequently it is necessary to run at a flow rate that is abnormally high compared with the genuine requirements for blowing gas.
The above-mentioned system with valves and compartments has also been used to generate different blowing forces across the width of the traveling strip, in order to be able to cause the strip to be inclined so as to obtain stability that is improved to a greater or lesser extent. Different blowing rates have also been used to generate strong blowing forces at the ends and weaker blowing forces in the center of the traveling strip, thereby making it possible to avoid dishing of said strip and prevent it from touching the boxes or the blow nozzles.
Proposals have also been made to use that valve and compartmenting system to adjust the transverse uniformization of the traveling strip by blowing more or less strongly against the strip. Under such circumstances, adjustment is performed manually and monitored by a pyrometric scanner.
Document JP-61 257429 A describes a set of two blow boxes with a steel strip for cooling traveling between them. The active face of each box presents through slots for blowing a cooling gas, and said face is fitted internally with two lateral flaps pivoting thereon, plane on plane, so as to vary the width of the slots in the travel direction of the strip, said width decreasing in the travel direction of said strip so as to exert cooling that is progressively more energetic in the central portion of the strip. It should be observed that both of the pivoting lateral flaps are secured to the active face of the box and that the edges of said flaps are always oblique relative to the travel direction of the strip. There is therefore no question of adjusting the width of the material, but only of varying the width of the cooling zone for a given width of strip.
Adapting to the width of the strip is disclosed in document JP 57-171626 A for cooling with water. In that document, the (sole) cooling box is fitted with spray nozzles having their inlets selectively fed by means of two pistons that can be moved transversely.
Such adaptation is also to be found in document GB-2 096 490 A using movable transverse sliders associated with slots for projecting a cooling liquid.
Document JP-58 185 717 A illustrates a system with screens (FIG. 5) serving to vary the width of the cooling zone on either side of an orthogonal midplane of the strip, but in association with boxes that can be inclined.
Document JP-63 077564A shows a complex system with transversely-movable sliders serving to feed the fluid injection nozzles selectively in order to take account of the width of the strip in question.
Finally, document DE-31 46 656 A describes a cooling tube having removable seals suitable for taking account of the strip in question.
There is thus a need for a device that is more flexible, in particular that is capable of responding easily and accurately during changes of strip width, and if possible of improving the gas blowing performance.